You won't find a perfect duplicate, even if you try to color-match. Hell, even paint batches from the original manufacturer will differ. Ask anyone who is a professional home painter or car body painter, and they'll tell you that the only way to ensure a perfect match across all your painted surfaces is to use a single mixed batch of paint and paint the whole thing all at once. That's just how it is.
Fortunately, white is one of the easiest to fudge so that discrepancies in color aren't as noticeable, but if you have a pearl or metallic finish that makes things more complicated. To get a good finish, you need to properly prep the surface, then prime it, then sand it, then paint it, sand it, paint it, sand it, paint it, sand it, put on clear coat, sand it, put on clear coat, sand it, and polish it. Doing a good job on auto paint is an extremely time- and labor-intensive process.